Good morning, gentlemen. 2000 C5 M6, brand spanking new clutch kit and throwout bearing with less than 1k miles, 75k on trans, lots of motor work. Running DOT4 fluid in clutch. Shifts are effortless with no grinding, BUT, sometimes at high RPM, it's a little difficult to get it into gear, but no grinding or strange noises or clutch slippage. Also, at times when in 1st or reverse it feels as if the the clutch/tranny is engaged partially when the pedal is to the floor and makes a bit of "buzzing" sort of grinding noise but goes away as soon as the clutch is either fully engaged or the car is put in neutral and then everything is normal. Also, when rolling in any gear at just about any speed and the clutch pedal is depressed and throttle is applied (revving it a little), the noise is heard until the same, either the clutch is re-engaged or you put it in neutral. Again, I've changed to DOT 4 fluid in the reservoir, it's a brand new clutch, I've tried aligning the shifter with the factory pin (pretty sure I did it right and noticed no change after). Could it be a bad slave cylinder? The syncros seem to be fine because there's no grinding going in or out of gears and the tranny seems fine because there's no trouble in any gear with the clutch engaged or even romping on it down the freeway or from a dead stop. Should I maybe try changing the tranny fluid out with a good synthetic like Amsoil or maybe try aligning the shifter again? The car is driving fine all day, but this noise is annoying and needs to be addressed. Thanks!!!!!!

Mikey

 

Might be time for a new clutch master cylinder.

 

You think so? What about a failing master cylinder would cause that, sir? I know they're relatively inexpensive comparatively speaking. I've seen that RAM has one that's adjustable for about $180. I also know they're a bit of a PITA to get to under the dash. Then again, the only thing that's not a PITA on these cars is burning expensive gas.

 

One of the fail modes of a master cylinder is not displacing its full capacity of fluid. This translates to not moving the slave its full travel. Are you running a stock clutch or aftermarket?

 

It's a factory Z06 clutch. As far as I know anyway. That's what I was told it was when I bought it. I know it's not a Spec or anything like that.

 

Do you have an idea on what year clutch it might be? There were some with issues with the self adjuster. The adjuster would over compensate and cause the issue you are experiencing.

 

Crap. I have no idea,buddy. Is there any way to tell without removing it? I got it from some place in Lubbock. I can look into it and try and find out. If the adjuster is the issue, how do I remedy that?

 

The more I think about it, the more I suspect a master cylinder issue. The clutch has been in the car for almost 1000 miles with not a single hiccup until now and with no fluid loss, I can assume I can rule out the slave for now. That and the master is 10 times easier and cheaper to replace first. Any thoughts?

 

Sounds like it's not fully disengaging, if the system is fully bled then there could be a problem with the master and it would be the easiest thing to replace with out pulling the clutch back out.

 

Honestly, I have no idea if he bled the system when it all got replaced. I know I haven't because I don't have a remote bleeder and no equipment to take that much apart to get the bleeder to do it myself. I guess the easiest thing to do seeing as I probably will have to pay someone to bleed it, is to just go ahead and buy a new master and have them tack on whatever extra to replace it at the same time.

 

Now I'm being told throwout bearing. When I make the car make the noise, it seems to be clearly coming form the front, not the rear where the tranny is. Sounds more and more like bearing vibration to me. I've heard a failing pilot bearing will chirp, so I'm assuming that since the noise sounds nothing like a chirp and isn't constant, it's not the pilot. Will pulling the inspection plate off of the bell housing allow me to diagnos a bad throwout bearing? If I have to pull eeeeeeverything out to replace a throwout bearing, I'll replace the slave, too but, I'd rather be sure before I do 12 hours worth of work or worse yet, pay someone to.

 

Does yours sound like this? LINK1

Or this LINK2

 

Niether, sir. It's more of a "buzzing", almost a grinding sound. It also isn't every single time you depress or release the clutch pedal either. It almost has to be the throwout bearing though. There's no clutch slippage, no trouble shifting when driving or noises. Only when you're either about to stop and have it in first after already moving a little in 1st, reverse and if you push the clutch on the freeway in any gear and give it gas. Never in neutral no matter where you have the clutch pedal.

 

Well, your last statement rules out it being the throw out bearing. Keep looking.

 

Uh oh, lol. Where else should I look?

 

It couldn't be that the throwout bearing is binding up so when it's in neutral, there's no resistance from the transmission when it binds and the clutch is trying to do it's job but it can't because the bearing is slowing down?

 

Well, believe it or not, I read through your entire thread again.

How long have you been driving manual corvettes?

All manual Corvettes, C5 and C6, will make a rattle almost buzz type noise during launch, especially during slow launches. The noise will start and as the rpm climbs it will fade away. Is this the noise you are talking about? If yes, this is normal. You can read about in the owner’s manual and on early Corvettes they even came with a video about it.

 

Well, that's the weird thing, it doesn't do it when you take off. Only if you move a few feet and slipped the clutch a little and then disengage the clutch to stop moving and when it's making the noise, it almost feels like the car is trying to lurch forward a little. Doesn't that sound like throwout bearing binding up? I've only had this car for a few months, but I've had 3 f-bodies with 6speeds in them and I've ridden in a couple c5's that suffered from the "normal" rattle that you're talking about.

 

F body to Y body are two different animals, really can’t compare.

The rattle noise I spoke of that is normal is the first torsional resonant mode of the propshaft. It can also be excited if the clutch disc is dragging between the pressure plate and flywheel when the clutch pedal is push in.

So, I’m back to thinking your problem is still master cylinder if the disc is in fact dragging. You can test for this by having the car in a flat parking lot. With the car in first gear, clutch pedal pushed full in, rev the engine to see if the car moves forward at all. If it does, it is time to replace the master cylinder.

 

I've actually tried that and if it's not making the noise, it doesn't even attempt to move with clutch pushed in, 1st gear and grabbing about 4k on the tach. When it makes the noise, it lurches forward slightly.

I knew the f-bodies aren't really the same in most aspects, just saying. I really appreciate all your help. This problem is seemingly more annoying than it is detrimental to driving the car, lol.